I am sure that many of you have heard of the OpenROV Project which involves building your own ROV from a kit. I am an experienced model builder with plenty of experience and a reasonably equipped workshop, but I was a little taken aback at the complexity of assembling the OpenROV from their kit of parts. It seemed to me to be a high school to college level project requiring a small team of experienced modelers to successfully put the OpenROV together though I could be wrong.
It appeared to me that there were a number of critical assembly requirements that had to be performed spot on as there was no going back to realign or reseal once the assembly was completed. Therefore I have been looking around to see if there might be an easier way to design and build a ROV similar to the OpenROV without having to perform some of the critical assemblies required to complete the OpenROV.
One area of the OpenROV design that I took exception to was the thrusters. They were not going to last very long when immersed in seawater due to the exposed bearings and stator/armature. To me this was a kind of deal breaker as to the questionable lifespan of these thrusters. I know that commercial thrusters are not cheap (think Seabotics or CrustCrawler) and the OpenROV project was just trying to overcome the high price of commercial thrusters with their homebrew design. Still the unknown lifespan of the OpenROV design did not leave me with a warm feeling to say the least.
Then came along Blue Robotics and their T100 Thruster KickStarter Project Link. Their design approach looks good and they have actually tested and characterized prototypes of the thrusters they will deliver to the pledgers. With the addition of the in-thruster water cooled ESC this design becomes very attractive in that it reduces the number of wire penetrations in the Water Tight Compartment (WTC).
Great! Now we have a source of reasonably priced thrusters so what is next? Well, that is where you, the ArduBoat members, come in.
Let's start thinking about the WTC, navigation controller, communication, power, ballast, buoyancy, etc. and attempt to come up with a reasonably priced ROV that the average ArduBoat member might want to consider building.
You are right about AC being the best method of power transmission, however the Pacific Intertie Link, that terminates north of Los Angeles, Ca, uses 1 million volts DC (+/-500Kv 2 pole) which allows the transmission of 1 Megawatt per Amp of current.
Tom C AVD
Just found this post, so I apologize for my late reply.
I've been working in the ROV industry for almost 10 years, built my own ROV's and acted as a consultant on 2 commercial ROV designs. I also develop software for the ROV industry full time. I've recently seen an OpenROV (version 2.7) in operation as well as the Blue Robotics T100 thrusters.
OpenROV: I agree with your analysis of the OpenROV: It is great for what it is intended for (as a learning project for high school or junior college students), but as a task worthy ROV, it fails miserably. There are just too many weak points in its design, some of which have already been mentioned.
Thrusters: The Blue Robotics T100, on the other hand, impressed me to be worthy of consideration. Similar to the exposed brushless motors of the OpenROV, the T100 is also based on an open motor, but at least they've attempted to build it of more "marine friendly" materials. Time will tell how long these last under typical operating conditions, but considering the cost savings (compared to commercially available oil compensated thrusters) it might be a risk worth taking.
Power: I believe that the future for powering mini / micro ROV's is self contained batteries. LIPO and other high efficiency batteries are becoming smaller, lighter and more affordable every day. Topside power will always have to fight the distance / power loss equation, where as on board batteries do not. Not having to lug around a portable generator to a launch site is a huge benefit, not to mention the additional safety factor by not sending power down a wire.
Navigation / Electronics: I think the current trend of putting a CPU in the ROV is over-kill / over-complication and is mostly motivated by a desire to make ROV controls "look" like a UAV. Don't get me wrong, I like the sexy look of a good HUD, but APM et al were designed for aircraft and consequently focus on data received from GPS. ROV's cannot use GPS and consequently rely almost entirely on depth and compass heading for navigation.
Sonar and Manipulators: What we really need next are an affordable Sonar and manipulator (grabber). What fish finder manufacturers like Humminbird, Lowrance and Garmin are offering for fishermen rivals what many ROV sonar manufactures offer. I can't wait for the day when I can add a forward scanning sonar to my ROV for under $1000 (or even $3000) and a manipulator for about the same.
Some great observations!
I am still waiting for my Blue Robotics T100 thrusters with the built-in ESC to begin my ROV Project.
I have received my three Blue Robotics T100 Thrusters with ESCs and have ordered an addition T100 Thruster and a 4" WTC kit.
The only drawback to using the ESC equipped thrusters is the ESC control cable that will require an additional hull penetration. Also, the control cable is around 3.5mm in diameter and the ready made hull cable penetrators are built for the 6mm diameter ESC power cable. However there are blank cable penetrators available so you can roll you own which I might consider doing as I have a vertical mill to drill the holes in the blank penetrators.
Most of the ROVs on the homebuitrovs.com website appear to use around four thrusters. Two thrusters for vertical movement and two thrusters for forward/backward/right/left movement.
However, it looks like the Blue Robotics BlueRov uses six thrusters which makes using T100 Thrusters with ESCs difficult in relation to the number of hull cable penetrators that will be required. Using just four thrusters with ESC control will require eight hull cable penetrators plus a vent plug and the control cable hull penetrators. So you can imagine what the WTC end plate will look like with the addition of four more hull cable penetrators.
Tom C AVD
Yes, using the "built in" B.R. ESC's will double the number of required hull penetrations, but on the other hand it takes all the space and heat that external ESC's generate and puts it in the water. That's the route I plan on going. There are a couple ways of handling the additional cables: One is to have a second 4" housing and use it for battery storage (my plan) or make a "junction box" just for the power connections. Any plastic box that has a rubber seal could be put to service for this. Filling it with mineral oil would increase it's depth capability also.
How many thrusters you use will depend on what you want the ROV to do: will it need to move laterally in current? go to great depths? tow a long tether or recover heavy items? Its really up to you. For my design I've limited the number of thrusters to 4, two forward/reverse and two vertical (angled at 40 degrees). I chose this thruster setup because:
1. The ROV will be battery powered and I need to limit the power draw to increase the dive time, and
2. I used vectored vertical thrusters so I can use them for some lateral movement.
I'm also choosing the T200 thrusters for my build. If you check the new charts on the B.R. site you'll see that the T200 is just a bit more efficient than the T100 thrusters. Better for battery power conservation and more thrust is always a good thing. ;)
I'm interested in any feedback you may have for the electronics boards you have. I'm shopping for a suitable solution for my build. I've seen most of what is out there. I do like the APM Mission Planner and would like to integrate that into my control system somehow. Even if just to use it while the ROV is on the surface.
You might want to reconsider using an APM2.6, but not for navigation, but for stability.
The IMU in the APM can provide stabilization input for a form of FBWA underwater to help keep the ROV stable without operator input?
I like your four thruster concept as I do not particularly have the need to move latterly. Angling the vertical thrusters at 40 deg is interesting and makes good sense for some lateral control.
I have an SRV-II submarine that uses only two thrusters, but they can be rotated in azimuth to act as either forward/backward thrusters or vertical thrusters. This assumes of course that the ROV is set up for neutral buoyancy at the required operating depth or the operator is always having to rotate the thrusters vertically to maintain his depth.
The idea of twin WTCs in an over/under configuration might work well to help reduce the hull cable penetration clutter and provide room for more batteries:-)
I plan to use my ROV in local lakes on the East Coast of Florida and around Captiva Island on the Gulf Coast in depths no greater than a 100 ft.
Tom C AVD
What sort of "stability" are you talking about? Keeping the ROV level? Maintaining station at a fixed location?
I was thinking of using a "tactical" grade CAT5e cable for the tether. "Tactical" grade usually has a heavier cover and is shielded. My hope is to use 1x twisted pair for comms and 1x twisted pair for video, leaving 2x twisted pairs for sonar and/or other expansion.
In a way yes. I was thinking about pitch and roll stability when on station underwater without operator intervention.
Shielded Cat 5 can get really stiff and you need to use the stranded pair version to improve flexibility. There is Cat 5 that can be buried, but it may not come in a stranded pair version. Stranded pair versions are usually used to make pigtails for interconnecting LAN hardware.
Since I plan to be on station in a boat over the target area, there will be no need for the ROV to navigate to the point of submergence.
Tom C AVD
In a "conventional" ROV design, the vehicle usually has some static stability, where the center of buoyancy is above the center of gravity. Smaller ROV's less so and larger ROV's typically more so. This static stability is a good thing and helps the operator maintain station and focus on a target during an inspection or other operation. There are a few exceptions to this, notably the AC ROV, Deep Trekker, AquaBotix and BlueROV (there may be others). It's my experience that these ROVs, although in some cases more maneuverable, are more difficult to keep focused on a target.
Since Blue Robotics has made a complete 4" dia WTC kit available on their website store I have been thinking about the configuration of my ROV Project
I am considering using two 4" WTC when using the T100 Thruster with the built-in ESC.
The lower WTC will contain the LiPo batteries and the ESC power cables will attach to that battery compartment end plate.
The upper WTC will contain the navigation controller and other electronic components and the ESC control cables with attach to the navigation compartment end plate.
The thinking here is if there is a battery fire, then the navigation controller will be isolated from the damage caused by the battery failure and it reduces the number of end cap penetrations in the navigation controller.
The navigation controller WTC will only have 8 end plate penetrations: 4 ESC control cables, 1 control cable, 1 instrumentation cable, 1 power cable and 1 pressure relief valve.
The battery WTC will only have 7 end plate penetrations: 4 ESC power cables, 1 instrumentation cable, 1 power cable and 1 pressure relief valve.
If I use the 10 penetration WTC end plates, this will give me room to add two additional T100 thrusters.
That sound smart to me. It will give plenty of room in the compartments as well. Something to note. After using the T 100 thrusters for about 35 hours with them running at about a 3 amp draw I have never felt the basic ESC's to be very hot at all. I did a continuous 1 hour run and then immediately checked them and was surprised at how cool they were. I guess it depends how hard the ROV is going to be run, but, I'm wondering if the water cooled ESC's are really necessary.
David R. Boulanger
That's the same result we generally have, especially when only drawing 3 amps. For typical ROV usage, the current draw won't be very high at all.
The T200s will make the ESCs warm when running at 20 amps, but I can't think of too many situations where that would be necessary.